The classification or “family tree” of electric machines today

ABSTRACT

At this time of great disruption, many engineers will take time to reflect on their work and studies. As it has happened in the past, improved understanding and new methods have emerged from periods of difficulty, and this will surely happen again. This engineering webinar series sponsored by JMAG and Powersys is intended as a contribution to this process. Prof. Miller begins by reviewing the entire family of electric machines, uncovering the theoretical and manufacturing reasons why machines are built and used as they are today. He draws particular attention to the unity of the family of AC drives, which includes the asynchronous induction motor and the brushless PM motor as well as the AC synchronous machines.

The profound influence of electronic control is made clear, not only in relation to its history but also for the present and the future. Equally the impact of modern permanent-magnet materials is shown in detail, and the question of scarcity is discussed. DC machines, universal motors, and the important classes of reluctance machines are shown to be full members of today’s family of electric machines with important roles. We hope the webinar will appeal to a wide audience. For anyone new to the industry, it can be used as an introduction. Students may find it helpful in sorting out the confusing array of different machine types. Specialists (including the expert users of sophisticated software tools) may like to take a break and enjoy a wider view. And experienced designers and users may compare their own reflections on the electric machine industry through this unifying review.

Program

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In this video Prof. Miller explains the close relationship between the circuit theory, the control theory, and the field theory of electric machines. After a brief review of the nature of performance calculations, we see how the concept of the space-vector unifies the physical principles and the control methods for DC and AC machines, and goes beyond the scope of classical teaching to include the power-electronic switching inverter. The space-vector concept is explained in detail alongside Park’s transform, which is used to deal with saturation in the important IPM motor, using the finite-element method in an extremely efficient way. The conclusion is that a set of modern software tools …

In this third seminar, we will be covering discussion regarding numbers of poles.This involves discussing the merits of a large number of slots per pole, the difference in magnetic circuits when changing the number of poles, and the relationship between the number of poles and inductance. All this and more is explained with a focus on the number of poles as the central theme.The number of poles provides the opportunity to re-examine electric machines from a new perspective. We look forward to your participation.

Noisy Lumpy Growling Effects in the Induction Motor

In this fourth seminar, we will be covering discussion regarding the parasitic torque and noise of induction motors.Factors that cause torque are shown through the analysis of the spatial harmonics of windings, and both the parasitic torque and noise of induction motors are explained based on the relationship between noise and torque irregularities. While a total comprehension of all the concepts covered in this seminar might be something of a challenge, referring to the Green Book should help forge a deeper understanding.

The Flux-weakening Phasor Diagram of the Brushless Surface-Magnet PM Motor

In this fifth seminar, we will be covering discussion regarding the phasor diagrams of SPM motors.This involves creating phasor diagrams from scratch, and using phasor diagrams in particular to describe the principle of weakening magnetic flux in the high speed regions of PM motors.Also referring to the Green Book should aid in a deeper understanding of these concepts.

Analysis of a Brushless Surface-Magnet PM Motor -Winding layout-

This sixth seminar begins discussion on analyzing the features of surface permanent magnet motors, introducing rules for drawing coils and methods for creating winding diagrams and estimating motor performance with winding designs.

Analysis of a Brushless Surface-Magnet PM Motor -Magnetic and Electrical calculations-

This seventh seminar sees the second discussion regarding surface permanent magnet motors, with magnetic and electrical calculations executed in accordance with classical theories.This involves calculating the time harmonic components of induced voltage, followed by the calculation of magnetizing inductance before a finer disassembly of the other inductances.

Preliminary Design of a 3-phase Induction Motor (Part 1: Stator)

This seventh seminar sees the second discussion regarding surface permanent magnet motors, with magnetic and electrical calculations executed in accordance with classical theories.This involves calculating the time harmonic components of induced voltage, followed by the calculation of magnetizing inductance before a finer disassembly of the other inductances.

Preliminary Design of a 3-phase Induction Motor (Part 2 : Stator winding design)

This ninth seminar consists of the second part of our continuing focus on induction motor design.In the first part we introduced the outer design of the stator, whereas this time we will be turning our attention to designing the stator winding.For this we will be using short pitch winding. This seminar will explain both why this was chosen, as well as information on the distribution factor.We hope that all those joining us will be looking forward to our next seminar, where the third part of this ongoing series will be talking a look at rotor concept design.

Preliminary Design of a 3-phase Induction Motor (Part 3 : Rotor)

This tenth seminar is Part 3 of designing an induction motor.The previous two seminars showed the process of determining the size of the motor and subsequently developing the stator design.This time the focus will be on rotor design.The workflow involves first determining the air-gap length, then the number of rotor slots and finally, the slot geometry.Guidelines for determining the design parameters are shown with the explanations.

Preliminary Design of a 3-phase Induction Motor (Part 4 : Equivalent circuit)

This eleventh seminar is Part 4 of designing an induction motor.In this seminar, the induction motor is modeled using an equivalent circuit, a practical tool for checking the basic characteristics of the design. Starting with an introduction of the equivalent circuit of the transformer, it explains the use of an equivalent circuit in the induction motor. We hope the seminar will be useful in understanding how to use an equivalent circuit in modeling the induction motor that rotates asynchronously with the rotation of the magnetic field.The seminar shows up to the stage where actual calculation of primary and secondary resistance are performed.

Preliminary Design of a 3-phase Induction Motor (Part 5 : Equivalent circuit reactances — Magnetizing reactance)

This twelfth seminar is Part 5 of designing an induction motor.In this seminar, we will try to calculate the magnetizing reactance in the equivalent circuit of the induction motor.The magnetizing reactance is one of the most important concepts in the induction motor theory.The seminar focuses on explaining magnetizing reactance by using both the classical theory and the finite-element method.

Preliminary Design of a 3-phase Induction Motor (Part 6 : Equivalent circuit; Stator slot-leakage reactance)

This thirteenth seminar is part 6 of designing an induction motor.The focus is on the stator slot-leakage reactance of equivalent circuits in induction motors. The leakage reactance is the most important concept in the theory of induction motors. It not only determines the maximum torque in the induction motor, but can be said to determine available level of torque at all speeds.In this seminar, leakage reactance is reviewed and described from the perspectives of both the classical theory and the finite element method.

Preliminary Design of a 3-phase Induction Motor (Part 7 : Equivalent circuit reactances — Rotor slot-leakage reactance, differential reactance, and end-winding leakage reactance)

This fourteenth seminar is part 7 and the final lecture on designing an induction motor.This lecture explains the leakage reactance in the equivalent circuit of induction motors. The calculation of the equivalent circuit impedance is completed here and we will use the equivalent circuit to check and evaluate the characteristics and performance of the inductance motor.

IPM Interior Permanent-Magnet Motor (Part 1 : The Rotor)

From this 15th seminar, we will be covering IPM motor design and this will be part 1, the rotor edition.Up until the last seminar, we completed the design of a 10kW induction motor. We will now change only the rotor to IPM. For comparison’s sake, the stator shape of the induction motor will be used as it is for the IPM motor.In this seminar, we will design the V-shaped rotor. I will introduce the historical changes in the rotor of permanent magnet motors and explain what each dimension is heavily dependent on.

IPM Interior Permanent-Magnet Motor (Part 3 : Open-Circuit EMF Ripple and Cogging)

In this 17th seminar, we will be covering discussion regarding the IPM motor open-circuit condition, where I explain the EMF and cogging necessary for evaluation in the open-circuit condition.First, we evaluate the EMF by focusing on the dips in flux-linkage that occurs as a result of the slot-openings, then similarly evaluate the cogging torque that occurs due to the stator slots.

IPM Interior Permanent-Magnet Motor (Part 2 : Open-Circuit Calculation)

In this 16th seminar, we will be covering discussion regarding IPM motor open-circuit calculations.We take for consideration an open-circuit where the rotor is inserted into the stator, and where no current is flowing in the stator coils. The ideal magnetic flux density distribution in the air-gap is calculated approximately with the magnetic equivalent circuit method, and FEA is used to check the harmonic component that occurs as a result of the stator slots, etc.Through the changes of the operating point of the magnet on its demagnetization curve, I then explain the effect of the leakage flux that occurs due to the air-gap and the bridges.

This 18th seminar is part 4 of the IPM motor and will cover the synchronous inductances and the phasor diagram.Synchronous inductances are determined by 3-phase to 2-phase conversion and characteristics such as current dependence of the synchronous inductances are explained. At the end of the seminar, we check the relationship between EMF, voltage drop in the dq-axis, and terminal voltage using phasor diagrams.

Synchronous Reluctance Motor (Synchronous inductance & phasor diagram)

In this 19th seminar, we will be covering the synchronous reluctance motor.As we previously used the stator core of the induction motor, similar to our previous work with the IPM, the seminar this time will explain the features of the synchronous reluctance motor as the induction motor and the IPM are compared each time.Because the rotor of the synchronous reluctance motor is actually rather fragile, this is investigated not only magnetically, but also evaluated in terms of mechanical strength.

Wound-field Synchronous Motor (1. Design and Open-circuit Operation)

In this 20th seminar, we will be covering the wound-field synchronous motor.As we have previously done before, the stator of the induction motor will be used as the stator of the wound field synchronous motor.The rotor of the wound-field synchronous motor has a field winding, not a magnet. The most notable feature is that field current can be changed, but it needs to be appropriately controlled.In this seminar we will design the rotor shape as I explain the feature of the wound-field motor.Next time we will discuss the EMF of the wound-field synchronous motor and its performance.

Wound-field Synchronous Motor (2. Open-circuit Operation)

ABSTRACTIn this 21th seminar, we will continue to study the wound-field synchronous motor.This time we will evaluate the open circuit characteristics of the wound field synchronous motor and focus particularly on the EMF. The EMF is evaluated from various aspects such as static magnetic flux distribution, flux linkage of each phase, search coil results for each teeth, etc.Next time we will discuss the synchronous motion of the wound-field synchronous motor.If you have any comments for Prof. Miller, please.Video run-time: 26:13Video with caption by YouTubeThese automatic captions are generated by machine learning algorithms, so the quality of the captions may vary.(If you do not have access …

Wound-field Synchronous Motor (3. Synchronous operation)

In this 22nd seminar, we will continue with the wound-field synchronous motor. This time we will apply currents to the armature and stator and calculate steady-state operation at rated speed and load. We will check the relationship between the armature and stator currents for each current phase and review the magnetic flux lines and magnetic flux density distribution in each current phase.

Wound-field Synchronous Motor (4. Synchronous operation & phasor diagram)

In this 23rd seminar, we will continue to cover discussion regarding the synchronous operation of the wound-field synchronous motor.This time, we will obtain the average torque from the results of static magnetic field analysis, then check the wound-field synchronous motor from various characteristics such as the relationship between the field current and the torque.We encourage viewing this video after having seen video 22, as this video follows that previous video very closely.

In this 24th seminar, we will be covering the Switched Reluctance Motor.Switch reluctance motors have projecting poles on both the stator and rotor, so it is termed “doubly salient”. This time, we will introduce the features of SR motors that carry DC current in one direction instead of AC sine waves.

In this 25th seminar, we will continue to discuss the Switched Reluctance Motor.This lecture will explain the procedure of calculating the average torque of the Switched Reluctance Motor using fundamental electromagnetic theory.It is important to comprehend magnetic saturation since inductance, which plays a significant role in understanding motor characteristics, is dependent on conditions such as magnetic saturation.Magnetic saturation is checked using the magnetic flux density contour and flux line.

In this 26th seminar, we will check the number of slots and poles focusing on the PM brushless motor. The waveforms of motor characteristics such as flux linkage, EMF, current, torque and terminal voltage are strongly influenced by the number of slots and poles as well as the ratio of slot per pole. In this video we will check how the numbers of slots and poles affect the layout of the windings.In the next video we will consider the coil span and look closer at the number of poles.

In this 27th seminar, we will continue our discussion from the previous 26th seminar, and the number of slots and poles will be discussed in this Part II session.I will explain the above topic by focusing on the pitch factor (chording factor) in this lecture.By listening to the previous 26th and the current 27th seminars, you will be able to get a comprehensive idea on calculating and understanding the distribution and pitch (chording) factors.

In this 28th seminar, I will explain the fields and windings.The field theory behind the winding theory, as well as the field calculation that comes after the windings have been designed, will be described in this lecture.For the winding factor, which is an important parameter related to the windings, its definition and the calculation method will also be explained.

Inductance Analysis of Electric Machines by Classical and Numerical Methods

In Video No. 29, we will discuss a very important topic of the inductance of electric machines, which is constantly in the mind of the machine designer and of the control engineers responsible for inverters and motion control.

In this 30th seminar, I would like to define and discuss the concept of magnetizing inductance. It is a term that we often encounter in connection with AC machines, especially in the design of these machines and in the classical theory.

In this 31st seminar, we will explain the torque ripple in the IPM. This time, we will focus on the saliency, which is a very important feature of IPM motors, and pay attention to the role of harmonics in reluctance torque.

In this 33rd seminar, I would like to discuss a rather theoretical idea which I have called “inherent saliency” or “innate saliency.”This saliency is very useful when comparing the difference in rotor geometry and is free from the effects of winding harmonics, slotting, and magnetic saturation.

Inherent saliency of the synchronous reluctance motor

In this 34th seminar,I would like to use the sine-distributed winding to study the inherent saliency of a synchronous reluctance motor.This video is a continuation of videos to 30 to 33, in which we developed the concept of the sine-distributed winding and showed how it can be modelled in JMAG.

Inherent saliency of the wound-field synchronous motor

In this 35th seminar, I would like to complete the series of examples in which we have used the sine-distributed winding to study the inherent saliency of various synchronous motors. The last example is the wound-field synchronous motor.This theory of the ideal model can be found in various conference and papers going back many decades.Nevertheless they explain the underlying concepts in machine design that remain important today.

In this 36th seminar, I would like to discuss the concept of leakage. I will explain the general characteristics of leakage flux in a magnetic device with a simple topology. In the next video, we will turn to a more quantitative approach and consider the topic of leakage inductance.

For the 37th to 40th seminars, I would like to develop the concepts of leakage inductance, mutual inductance, and coupling coefficient.In this Video 37, labeled “Part 2”, we’ll begin by calculating the magnetic field and making a few simple checks.In the next seminar, we will use the same field calculation to extract the values of the self- and mutual inductances and the coupling coefficient k.

Leakage Inductance, Mutual Inductance, Coupling Coefficient and Equivalent Circuits (Part 3 : L M and k)

This 38th seminar is Part 3 of a short series of videos on leakage flux, leakage inductance, coupling coefficient and equivalent circuits.We can check the self-inductance L, mutual inductance M, and the coupling coefficient k.Additional post-processing functions for calculating engineering parameters like inductance are not used. Here we will use the most simplest definition, the flux-linkage per ampere.

This 39th seminar is Part 4 of a short series of videos on leakage flux, leakage inductance, coupling coefficient, and equivalent circuits.In the previous video, we ended up with an ideal T equivalent circuit for the example 2-winding transformer.In this video, we will generalise the equivalent circuit rigorously and examine some important variants that arise from the apportionment of leakage inductance between the primary and secondary.

This 40th seminar is Part 5—the last part—of a short series of videos on leakage flux, leakage inductance, coupling coefficient, and equivalent circuits.What we will see in this video—even for a relatively simple physical device—is that the classical equivalent-circuit model has some notable weaknesses in the presence of magnetic saturation.We will see how the finite-element method can be used to expose and also resolve the uncertainties inherent in the classical equivalent-circuit model.

In this 41st seminar, I would like to discuss the interpretation of certain boundary conditions, the ones that were the subject of Engineer’s Diary No. 61.Here I will use a cable duct to explain the interpretation of boundary conditions.There are many instances where understanding boundary conditions can help in the interpretation of physical phenomena and the choice of suitable boundary conditions in analysis and simulation.

In the last two seminars, we considered a magnetostatic solution with DC excitation in the two busbars, but in this seminar, we will extend the study to AC conditions with AC excitation.We will proceed to evaluate the differences in magnetic flux density and current density due to differences in duct material and frequency.

In the last two seminars, we considered a magnetostatic solution with DC excitation in the two busbars, but in this seminar, we will extend the study to AC conditions with AC excitation.We will proceed to evaluate the differences in magnetic flux density and current density due to differences in duct material and frequency.

In this 44th seminar, we will extend our study of eddy-currents in the walls of a cable duct, which we began in the previous seminar.The aim is to examine the effects of frequency and geometry on the behaviour of the eddy-currents.We also quote the contents of Engineer's Diary No. 64, so be sure to check out Engineer's Diary as well.

Inductance : Fundamental theory and practical aspects in analysis

In this 45th seminar we will explain inductance. Inductance is a “terminal” quantity that can only be measured at the terminals of a circuit, much like resistance, capacitance, EMF, etc. Here we will explain inductance in terms of both its theoretical and practical aspects.

This 46th seminar shows a graphical representation of harmonic interactions described by the classical mathematics of Fourier series.We display some of the ideas in the harmonic analysis of the waveforms of flux and ampere-conductors in AC machines such as the brushless PM AC motor.Many of these also apply to induction motors, so we will also introduce them during asynchronous operation.

As in the 46th seminar, the 47th seminar examines the graphical representation of harmonic interactions described by Fourier series. We will represent the basic phenomena of rotating magnetic fields graphically and confirm the mechanisms that produce the torque as well as visualize the harmonic components. The next seminar will look at time harmonics in the current waveform and unbalanced operation.

The 48th seminar looks at the time harmonics in the current waveform and unbalanced operation. The final demonstration examines the space harmonics, with no time harmonics in the phase current waveforms.These three seminars illustrate the necessity of analyzing higher harmonic components of the Fourier series to understand what is going on in the complex process of torque production in AC machines.

This video uses JMAG to look at air-gap sheer stress and torque.We can model the physical reality in JMAG to visualize the interactions between the stator and rotor.In this way, JMAG finite element analysis complements classical theory to give us a deeper understanding of motor behavior.

The 50th seminar entitled Per-unit Systems explains ways to express numerical values in complex systems and the practical day-to-day rules used in power system analysis.

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The Green Book:
“Design of Brushless Permanent-Magnet Machines”

Authors: J.R. Hendershot & T.J.E. Miller.
This 822-page brushless machine design book is generously illustrated in color as the authors have tried to catch up with the progress over the last 16 years of PM bushless machine design and development since their well-known 1994 book. Almost the entire work is the direct result of intensive consulting by the authors, in collaborating with many of the leading producers of brushless permanent-magnet machine products worldwide. The book was written with a focus on actual engineering practice and tries to deal with most of the questions that arise on a daily basis in PM brushless machine design. The authors’ partnership is a long-standing combination of theoretical, practical and consulting experience, while the book with its rich illustrations of industrial products celebrates the rich engineering accomplishments of design engineers from all over the world.

The Blue Book: “Design Studies in Electric Machines”

Authors: J.R. Hendershot, T.J.E. Miller.
This book is written for engineers concerned with the design and development of electric machines. It addresses two aspects of the modern design environment, in which powerful software tools are widely used: 1. How should we start a new design to meet a given specification. 2. How can the classical theory inform and support the design process? Some answers are attempted through a series of numerical design examples, including the surface-magnet motor (SPM), the interior-magnet motor (IPM), the asynchronous induction motor, the synchronous reluctance motor, the wound-field synchronous motor, and the switched reluctance motor. After the SPM, all the remaining motors are designed to the same AC drive specification with many common parts. Working with numerical design examples, the book (a) provides a platform for the use of CAE tools, starting with the same geometry, winding layout, etc so that more difficult aspects can be studied. (b) uses the finite-element method to help with several basic classical calculations, greatly improving the accuracy; and (c) presents and explains many of the theoretical principals of electric machine design without overburdening the subject with pure theory. The use of numerical design examples helps to keep the length of the of the book to a manageable scale.